The present invention relates generally to building of structures of concrete, and more particularly, to an improved vibrator head adapted for use with a lightweight, portable concrete vibrator.
It is a well known principle that the integrity of concrete structures is improved by making sure that the wet concrete poured into the form is substantially homogeneous; that is with the aggregate spread and evenly distributed and substantially all voids or air pockets eliminated. To do this, it is common practice to insert a vibrating head into the wet concrete within the retaining form. As the head is moved up and down and around the form and between the grid of reinforcing bars, pockets of aggregate or voids are eliminated. In my co-pending U.S. patent application, Ser. No. 09/233,801, Jan. 19, 1999 and entitled xe2x80x9cConcrete Vibratorxe2x80x9d, now U.S. Pat. No. 6,155,708, issued Dec. 5, 2000, I disclose and claim an improved vibrator that includes such a head and driven by a light-weight gasoline motor connected through a flexible drive cable within a sheath. The vibrator of that patent application represents a substantial improvement over prior art devices in assuring the proper spreading of the aggregate and elimination of the voids in the wet concrete. As disclosed, this desired result is accomplished by providing an intense, reasonably high frequency and amplitude vibration to the concrete from the vibrator head. This prior application is incorporated in the present application by reference.
As set forth in U.S. Pat. No. 6,155,708, a variety of rotor shapes are disclosed in the prior art. Typically, such as shown in the U.S. Pat. No. 4,057,222 to Lyle, the rotor is a standard metal bar with approximately one-half removed along the longitudinal axis. The rotor has stub shafts at each end for mounting in a metal casing by dual roller bearings mounted at both ends. A similar arrangement is illustrated in the U.S. Pat. No. 3,042,386 to Wyzenbeek. While this type of mounting has proven successful, additional improvement in the rotor and its mounting is possible. It is particularly desirable to provide enhanced vibration for a particular rotor mass, and without an increase in speed from my previous design, while at the same time assuring that the rotary mounting of the rotor is stable and secure. Improvements in durability, long life and low maintenance cost are also desirable.
Improving the efficiency of the vibration to provide better aggregate spreading and filling of the voids and air pockets has been attacked from many directions in the past. This fact is attested by the concepts shown in the patents described as background in U.S. Pat. No. 6,155,708, and many others. Increasing the intensity of vibration in a concrete vibrator of the type disclosed in U.S. Pat. No. 6,155,708 to accomplish the improved results while maintaining the reduced speed of rotation is important. If successful, such a design change would further enhance the ease and efficiency of use of the concrete vibrator by the worker, thus providing still further increases in productivity and reduction of fatigue during use. At the same time, it is desirable to simplify the eccentric rotor to further reduce the initial cost and to ensure that the maintenance requirements are minimized and the expectant life of the head is extended. Also, a guide line must be that any new vibrator head is adapted for use in the concrete vibrator unit of U.S. Pat. No. 6,155,708.
With the above needs for improvement of the vibrator head in mind, it is a primary object of the present invention to provide a head that is more effective in spreading and distributing the aggregate and wet concrete in a form to thereby enhance the integrity of the concrete structure, and in doing so to overcome the above described limitations and disadvantages of the prior art in a unique and very desirable way.
It is another object of the present invention to provide a concrete vibrator head that provides extended eccentricity of the rotor to substantially its full length so as to produce the enhanced vibration of the rotor mass.
It is still another object of the present invention to provide a vibrator head that is not only low in cost, but also simplifies the structure reducing the potential maintenance over the life of the head.
Another object of the invention is to provide support for the rotor during its circular path of movement by a fluid bearing.
Additional objects, advantages, and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, there is provided an improved vibrator head for a concrete vibrator of the type for evenly distributing the aggregate and filling voids in wet concrete poured in a form for concrete structures. The vibrator head is made more effective for enhanced vibration, has a fluid bearing and is further simplified from the head disclosed and claimed in U.S. Pat. No. 6,155,708 and all other prior art designs.
The vibrator head of the first embodiment of the present invention includes a hollow casing and a substantially full length eccentric rotor mounted therein. The rotor is supported at a first or proximate end by conventional bearing means, such as a pair of roller bearings. A drive shaft imparts rotary motion to the rotor and is designed to be driven through a flexible shaft.
The rotor includes a curved or arcuate segment along one of its sides that extends in an arc of approximately 120xc2x0. The centroid of the mass of the rotor is such as to provide a highly effective vibratory action as the rotor is rotated. It is desirable that the rotor strength is maintained to resist lateral flexing within the casing.
The rotor is machined from cold rolled steel that provides the desired mass along with reasonably good machining properties. Alternative approaches, such as casting the metal or other relatively high density material to form the rotor are considered to be equivalent. The rotor includes a pintle or stub shaft at the first end of the rotor for mounting the dual roller bearings. The manner in which the high strength of the rotor is obtained, is set forth and claimed in U.S. Pat. No. 6,155,708.
According to one feature of this first embodiment of the present invention, the stub shaft and the dual roller bearings at the second or distal end (non-drive end) are eliminated. Instead, a simple bushing is attached to the curved segment. The bushing is fabricated of disparate material, that is, a material of different molecular structure than the casing so that there is minimal affinity for wear.
A lubricant, preferably 10W or 20W motor oil, or equivalent, such as other high quality hydraulic fluid with similar lubricating and viscosity rating, is in the casing. It forms a thin, high pressure film between the support bushing and the internal surface of the casing. The high pressure, at about 70-80 lbs/in2, is generated by the rotation of the rotor and the squeezing of the oil between bushing and the casing due to the centrifugal force. The spacing of approximately {fraction (1/64)} inch works well. At 5,000-7,000 rpm, the rotor in this embodiment balances itself on the hydraulic film. There is in effect a counteracting force in this pressurized film that offsets the centrifugal force at the bushing and keeps the rotor centered. In addition, the space of approximately {fraction (1/32)} inch along the remainder of the rotor forms an oil film at about 35-40 lbs/in2 to provide support bearing assist, and at least partially unload, the dual roller bearings at the first end.
The cost of the vibrator head is minimized since the dual roller bearings at the second end are eliminated, along with the central stub shaft upon which these bearings are usually held. Also, since substantially the entire length of the rotor of the vibrator is eccentric, enhanced vibratory action is gained for a given size of vibrator head.
Preferably, the bushing forming the high pressure film for supporting the second end of the rotor is brass, although other disparate materials, including other metals or plastics can be used. Any equivalent material that has a molecular structure sufficiently different from the steel of the outer casing to prevent galling, especially during the time the rotor is getting up to operating speed or slowing down, can be selected. Of course, the casing itself can be fabricated of other materials, even rigid, high strength, high density polyethylene or the like, if desired.
In accordance with this first embodiment, the bushing preferably extends only along the arc of the curved segment of the second end formed by the rotor. Of importance, the bushing and rotor both include a leading bevel edge to assist in capturing the lubricant and forming the thin film as the rotor rotates.
Furthermore, the bushing includes an axially extending guide edge that mates with a shoulder on the internal surface of the casing. Again, a thin film of oil or other lubricant is formed between the edge and the shoulder to assure proper low friction, guiding relationship. The bushing is brazed or soldered to the rotor along the arc to provide a fixed attachment. Alternatively, high strength adhesive or equivalent attachment means can be used, if desired.
The proximal or first end of the vibrator head is formed by a drive end cap that supports the drive cable having the coupling for connection to the drive shaft of the rotor. At the second end, a distal end cap is provided and forms the peripheral internal surface of the casing for cooperation with the bushing. The guide shoulder is also formed on the internal surface on this end cap. The rotor end with the bushing mating with these surfaces of the end cap is highly stable in both the radial, as well as the axial direction when driven at the desired rotor speed range of approximately 5,000 to 7,000 rpm. The entire length, including the section of the rotor for attachment of the bushing, is eccentric so that the eccentricity is maximized and the resultant vibration during operation is enhanced. The cost is reduced significantly since the usual stub shaft and dual roller bearings at the distal end are eliminated.
In a second embodiment of the invention, single roller bearings replace both the bushing on the second end of the rotor, and the dual roller bearings on the first end. These bearings provide ease of rotation at the relative slow speeds of the rotor as it accelerates up to operating speed and decelerates during stopping. At a spacing of the outer surface of the rotor in the range of {fraction (1/64)}-{fraction (1/32)} inch from the inside of the casing, the oil film that builds up has a hydraulic pressure in the range of 35-80 lbs/in2 that efficiently resists the centrifugal force. This action at least partially unloads the single roller bearings. The bevel on the leading edge of the rotor serves to trap the oil along the full length of the rotor in order to form the supporting high pressure film. The beveled edge thus extends substantially along the full length of the rotor.
Still other objects of the present invention will become readily apparent to those skilled in this art from the following description wherein there is shown and described two preferred embodiments of this invention, simply by way of illustration of two of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments, and its several details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.